Effects Of PH On The Formation Of PIC Micelles From PAMAM Dendrimers

Polyion complex micelles(PIC micelles),novel nanomaterials assembled from oppositely charged polyelectrolytes by electrostatic driving,are widely applied as functional nano-carriers in a broad range of fields covering drug delivery,bio-imaging,catalyst,etc.due to their unique core-shell structure and loading environment.The formation of functional PIC micelles from dendrimers has attracted great attention in recent years for the reason that dendrimers represent ideal assembly units of PIC micelles with controllable structure and size.Besides that,their branched structure can not only load functional molecules,but also improve the stability of PIC micelles against salt.In this work,we investigate the effects of pH on the charge-driven assembly of amine-terminated PAMAM dendrimers and the formation of PIC micelles.PAMAM dendrimers contain surface and interior weakly basic amine groups with different pKa,so the charge amount and distribution of PAMAM dendrimers depend on the protonation of amine groups at different pH.Based on dynamic and static light scattering as well as transmission electron microscope(TEM),the effects of pH on the assembly of PAMAM dendrimers and PSS92-b-PEO113 diblock copolymers and the formation of polyion complex micelles have been investigated.The main research contents and findings are as follows:1.Formation of polyion complex micelles by assembly of PAMAM dendrimers and diblock copolymers has been investigated.Linear diblock copolymer PSS92-b-PEO113 synthesized by reversible addition-fragmentation chain transfer polymerization(RAFT)was applied as the negative polyelectrolyte.Different methods for preparating micelles were studied,which laid a good experimental foundation for the subsequent assembly and formation of PIC micelles.2.Formation of G3 PAMAM-based PIC micelles at different pH(pH 7,5 and 3)with PSS92-b-PEO113 has been studied,with focus on the pH effects on the structure and salt response of PIC micelles.The results reveal that the pH change from pH 7 to pH 3 does not affect the particle size and size distribution of PIC micelles,but influence the stability of micelles.The PIC micelles formed based on assembly of PAMAM surface charge at pH 7 show higher stability against salt.3.The effect of dendrimer generation on the formation of PIC micelles has been discussed.At pH 7,the assembly based on the surface charge of PAMAM dendrimers from multiple generations(G2,G3,G5,G7)leads to well-defined micelles with high stability against salt.At pH 3,both the interior and surface charges contribute to the assembly and the micellar size increases with increasing generation.Moreover,such micelles are sensitive to ionic strength,namely,increasing salt concentration results in formation of elongated(G2-G5)or bigger(G7)aggregates.